This invention relates generally to methods and apparatus for cementing a casing in a wellbore, and more specifically is directed to methods and apparatus for utilizing float equipment inside casing used to drill a wellbore.
There are a variety of known methods for drilling wellbores to intersect with one or more hydrocarbon-producing formations for the production of oil and/or gas. One known procedure, and an increasingly common procedure for drilling a wellbore utilizes the casing string that will be cemented into the wellbore as the drill string. When a wellbore is drilled utilizing casing as the drill string, the wellbore is drilled to a desired depth, and the casing is typically pulled upwardly a distance from the bottom of the drilled wellbore. The drill bit on the lower end of the casing is then blown off using an explosive charge on a wireline, or is disconnected from the casing by other means known in the art.
Once the drill bit has been removed from the lower end of the casing, mud or other circulating fluids may be circulated through the casing. A bottom cementing plug can then be displaced into the casing ahead of the cement. The bottom cementing plug is allowed to pass through the open lower end of the casing and cement passes around the lower end of the casing upwardly into the annulus between the casing and the wellbore. Once the desired amount of cement has been displaced into the casing, a top cementing plug is placed in the casing behind the trailing edge of the cement. The top plug and the cement therebelow are urged downwardly in the casing by drilling mud or other known displacement fluids. Once the desired amount of cement has been placed in the annulus between the casing and the wellbore to cement the casing in the wellbore, which may occur either before or after the top cementing plug exits the casing, flow of the displacement fluid is stopped. Pressure is maintained utilizing a valve system at the surface, typically in connection with a plug container. Prior to conducting any further operations or procedures, it is generally necessary to wait several hours to insure that the cement is adequately set up prior to removing surface equipment, such as the plug container, and then reassembling the wellhead. Although such procedures exist for drilling with casing and then cementing the casing in a wellbore, the time loss is significant and costly. Thus, an improved apparatus and method for drilling with casing and cementing casing in a wellbore is needed.